D. Majumdar

A comparative theoretical study of bonding in UO2++,UO2+,UO2,UO2−, OUCO, O2U(CO)2 and UO2CO3

Abstract Extensive ab initio calculations have been carried out to study the structure and bonding characteristics of UO2++,UO2,UO2+,UO2−,OUCO,O2U(CO)2, and UO2CO3 using various methods including complete active space multiconfiguration self consistent filed (CASMCSCF) and multireference singles plus doubles configuration (MRSDCI) techniques. The calculated vibrational frequencies of these species are compared with the matrix spectra of Andrews and coworkers. The nature of bonding in these species is discussed.

Theoretical study of aqueous uranyl carbonate (UO2CO3) and its hydrated complexes: UO2CO3.nH2O (n = 1-3)

Abstract Extensive ab initio calculations have been carried out to study the structure and bonding of hydrated UO 2 CO 3 complexes using state-of-the-art techniques. The structures of aqueous UO 2 CO 3 and its hydrated complexes have been further studied by considering the solvent as a polarizable continuum dielectric. The calculations have been carried out using polarization continuum, self-consistent isodensity polarizable continuum model, and conductor like screen models. The calculated uranyl frequencies of the hydrated UO 2 CO 3 have been compared with the available vibrational frequencies and the nature of water binding has been analyzed using energy decomposition techniques.

Spectroscopic properties of lead trimer (Pb3 and Pb3+): Potential energy surfaces, spin–orbit and Jahn–Teller effects

Spectroscopic properties of the low-lying electronic states of neutral, cationic, and anionic lead trimer (Pb3) are investigated. We have obtained the bending potential energy surfaces of several electronic states of Pb3 and Pb3+ both with and without spin–orbit coupling. These computations were carried out using high level techniques that included electron correlation effects and spin–orbit coupling simultaneously using a multireference relativistic configuration interaction (RCI) scheme in the double group, subsequent to complete active-space–multiconfiguration self-consistent-field (CAS–MCSCF) computations. We have computed the equilibrium geometries, vibrational frequencies, excitation energies, atomization energies, ionization potentials, and adiabatic electron affinities. Our computations facilitated the assignment of the anion photodetachment spectra of Pb3− and explained the “closed-shell singlet like” structures in the observed photodetachment spectra. Our computations show that spin–orbit coupli...

A comparative theoretical study of uranyl silicate complexes

Extensive ab initio calculations have been carried out to study the equilibrium structure, vibrational frequencies, and bonding characteristics of various uranyl (UO 2þ 2 ) and uranyl silicate complexes (UO2SiO4H2 and UO2Si2O7H4). The geometry optimization and calculated vibrational frequencies are discussed and compared to experiment. We have found two types of bridged structures for uranyl silicates consistent with the EXAFS study of U(VI) sorption onto silica gel, which revealed two different bridged structures at different U loadings. 2003 Elsevier Science B.V. All rights reserved.

Theoretical study of the electronic states of small cationic niobium clusters, Nbn+ (n=3–5)

Geometries and energy separations of the various low-lying electronic states of Nbn+ (n=3–5) clusters with different structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field (CASMCSCF) method followed by the multireference singles plus doubles configuration interaction (MRSDCI) that included up to 13 million configuration spin functions have been used to compute several electronic states of these clusters. A 5A2 isosceles triangle geometry in C2v symmetry and a 2A′ pyramid structure in Cs symmetry are computed as the ground states of Nb3+ and Nb4+ clusters, respectively. In the case of Nb5+, a 1A′ state of distorted edge-capped tetrahedral structure (in Cs symmetry) was found to be the ground state. We also compared our MRSDCI results with density functional calculations. The dissociation and atomization energies have been calculated at the MRSDCI level and the results have been found to be in agreement with experimental findings.

Theoretical study of the electronic states of niobium trimer (Nb3) and its anion (Nb3

Geometries and energy separations of the various low-lying electronic states of niobium trimer (Nb3) and its anion (Nb3−) with triangular and linear structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method followed by multireference singles plus doubles configuration interaction (MRSDCI) that included up to 48 million configuration spin functions have been used to compute several electronic states of these clusters. The geometries of ground and excited states of Nb3 and Nb3− are triangular. The ground states of both Nb3 (2B1) and Nb3− (1A1) have been found to be of low spin. The low-lying electronic states with degenerate symmetries in the D3h group are distorted to the C2v structure (from the ideal D3h) due to the Jahn–Teller effect. On the basis of the energy separations of our computed electronic states of Nb3, we have assigned the observed photoelectron spectrum of Nb3−. We have also compared our MRSDCI results with density functional ca...

Interaction of benzene (Bz) with Pt and Pt2: A theoretical study on Bz–Pt2, Bz2–Pt, Bz2–Pt2, and Bz3–Pt2 clusters

Extensive ab initio calculations have been carried out on benzene (Bz)–platinum complexes (Bz–Pt2, Bz2–Pt, Bz2–Pt2, and Bz3–Pt2) using a variety of computational techniques. Both physisorbed structures and energetically lower chemisorbed species were found. Complete active space multiconfiguration self-consistent field (CASMCSCF), multireference singles and doubles configuration-interaction (MRSDCI), density functional (DFT), and Moller–Plessett second order perturbation (MP2) calculations were employed to predict Bzm–Ptn structures. While the DFT and MP2 calculations also consistent with the MRSDCI techniques predict chemisorbed structures to be lower, the CASMCSCF method seems to favor physisorbed structures. The effect of spin-orbit coupling on the binding energies of complexes with the Pt atom and the Pt2 dimer were considered. The computed dissociation energies are consistent with the relative abundance of these clusters found in the time-of-flight mass spectra. The low-energy staircase structures of...